In general, a plurality of semiconductor chips or semiconductor packages are used to control a system incorporating a power transistor with a high breakdown voltage. In this regard, FIGS. 29 to 31 each show a block diagram of a semiconductor device that controls a power transistor PTr with a high breakdown voltage. In such a system as shown in FIGS. 29 to 31, a control circuit 101, which generates a control signal for the power transistor PTr, and a gate drive circuit 103, which drives the power transistor PTr, are connected via an insulating interface 102.
In order to adjust electric energy supplied to an electric motor, lighting equipment, or the like, the control circuit 101 generates a control signal for the power transistor PTr by means of pulse width modulation (PWM), for example. The control circuit 101 mainly includes a microcontroller, a PWM circuit, a timer circuit, a comparator, and an analog-to-digital conversion circuit. The gate drive circuit 103 detects a change in impedance of a reception-side phototransistor of a photocoupler, for example, to control the gate terminal of the power transistor PTr.
The insulating interface 102 includes an AC coupling element that couples the control circuit 101 and the gate drive circuit 103 in an alternating manner while electrically insulating them from each other, and transmits only necessary information such as a control signal. FIG. 29 shows a configuration in which a photocoupler used as the AC coupling element. FIG. 30 shows a configuration in which a magnetic coupler (for example, a transformer) used as the AC coupling element. FIG. 31 shows a configuration in which a capacitive coupler (for example, a capacitor) used as the AC coupling element. In the case where a transformer or a capacitor is used as the AC coupling element, a modulation circuit and a demodulation circuit are used to transmit signals through the AC coupling element. Patent Literatures 1 to 13 disclose an example in which a transformer is used as the insulating interface 102. Patent Literatures 3 and 14 disclose an example in which a capacitor is used as the insulating interface 102.
In FIGS. 29 to 31, semiconductor substrate areas are hatched and semiconductor package areas are surrounded by dashed lines. As shown in FIGS. 29 to 31, it is necessary to electrically insulate the circuits formed on, the control circuit 101 side from the circuits formed on the gate drive circuit 103 side. Accordingly, the insulating interface requires two semiconductor substrates, regardless of the coupler to be used. In other words, as shown in FIGS. 29 to 31, in the system configured using the insulating interface 102, the number of semiconductor substrates and the number of semiconductor packages are undesirably increased. Such a problem is evident when a motor drive control system or a lighting system is constructed using the insulating interface.
FIG. 32 shows a block diagram of a typical motor drive control system, and FIG. 33 shows a block diagram of a lighting system. The motor drive control system shown in FIG. 32 is a system for driving a three-phase electric motor. The system includes six power transistors PTr for driving the three-phase electric motor. A power supply circuit 110 for supplying high-voltage power is provided to the power transistors PTr. This power supply circuit 110 is an AC/DC conversion circuit that generates a DC power of 0 to 1 kV from AC power of 100 to 250 V. The power supply circuit 110 performs AC/DC conversion through a switching operation of the power transistors PTr. That is, it is necessary for the motor drive control system shown in FIG. 32 to control eight power transistors PTr. Thus, eight insulating interfaces 102 and eight gate drive circuits 103 are required according to the number of power transistors PTr. Accordingly, in the motor drive control system shown in FIG. 32, assuming that the number of the power transistors PTr to be controlled is represented by N, 2N+1 number of semiconductor packages and 3N+1 number of semiconductor substrates are required.
The lighting system shown in FIG. 33 includes a light-emitting diode serving as a lighting element 122. The lighting system shown in FIG. 33 has a function for adjusting an illuminance of the light-emitting diode. When a light-emitting diode is used as a light-emitting element, the illuminance thereof is proportional to a current flowing through the element. Accordingly, a method is employed in which the amount of current flowing through the light-emitting diode is controlled to a desired value. In the example shown in FIG. 33, a shunt resistor Rshunt for detecting a current flowing through the light-emitting diode is prepared to perform a negative feedback control so that a voltage generated in the shunt resistor Rshunt is set to a desired value. In the lighting system shown in FIG. 33, the insulating interface 102 is used to perform such a negative feedback control.
The control circuit 101 shown in FIG. 33 compares the voltage obtained from the shunt resistor Rshunt with an illuminance adjustment signal. Then, depending on the magnitude of the signal, the PWM circuit changes a duty ratio of a pulse signal. For example, when the voltage obtained from the shunt resistor Rshunt is lower than the voltage of the illuminance adjustment signal, the PWM circuit increases the duty ratio of the pulse signal (increases the pulse width). As a result, a voltage is applied to a primary coil of a transformer 121 for a longer time, and greater power is supplied from a secondary coil, so that the voltage obtained from the shunt resistor Rshunt increases. On the contrary, when the voltage obtained from the shunt resistor Rshunt is higher than the voltage of the illuminance adjustment signal, the PWM circuit decreases the duty ratio of the pulse signal (decreases the pulse width). As a result, the power supplied from the secondary coil of the transformer 121 decreases, and thus the voltage obtained from the shunt resistor Rshunt decreases. A power supply circuit 120 performs such a negative feedback control to thereby output a desired voltage.
At this time, in the lighting system, the control circuit 101, the insulating interface 102, and the gate drive circuit 103 are used to control a power MOS transistor PM based on a PWM signal. This is because a PWM control signal cannot be generated in a circuit having a high breakdown voltage due to its low operation speed and it is necessary to manufacture the gate drive circuit 103, which requires a high breakdown voltage, and the control circuit 101, which requires a high operation speed, by different processes. That is, also in the lighting system shown in FIG. 33, at least three semiconductor packages and four semiconductor substrates are required to control the power MOS transistor PM.
As shown in FIGS. 32 and 33, in the system that requires an insulating interface, the number of semiconductor substrates and the number of semiconductor packages are undesirably increased. In this regard, Patent Literature 15 proposes a hybrid IC having a configuration in which a pulse control circuit, a transformer, and a gate drive circuit are mounted in a single package. The use of this hybrid IC makes it possible to reduce the number of semiconductor packages of the system using an insulating interface.